An Introduction to Behavior-Driven Development (BDD) with Python and Behave

1. INTRODUCTION TO BDDINTRODUCTION TO BDD
BEHAVIOR DRIVEN DEVELOPMENTBEHAVIOR DRIVEN DEVELOPMENT
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2. 2 . 1

3. whoamiwhoami
Juan Ignacio Rodríguez de león
@jileon en Twitter
Backend developer en OctopusLabs
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4. WE ARE HIRINGWE ARE HIRING
More info at:
https://octopuslabs.com/careers
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5. HOW IS THIS TALK STRUCTURED?HOW IS THIS TALK STRUCTURED?
Presentation (Finished!)
Teory
Practice
Libraries, tools,
recomendations...
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6. THEORYTHEORY
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7. In theory, there is no difference
between theory and practice. In
practice, there is.
--
Benjamin Brewster
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8. WHAT IS BDDWHAT IS BDD
As stated by wikipedia:
... an extension of TDD that makes use of a simple, domain-specific scripting language
structured like natural language statements to ensures all development projects remain
focused on delivering what the business actually needs while meeting all requirements.
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9. manman
WATH IS BDDWATH IS BDD
As stated by wikipedia:
... an extension of TDD that makes use of a simple, domain-specific scripting language
structured like natural language statements to ensures all development projects remain
focused on delivering what the business actually needs while meeting all requirements.
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10. TLDRTLDR
They are tests. As in TDD, we use test to drive the
design of the so ware
Usually, on a higher level than TDD
Written in a natural lenguage , like English
Example
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11. TLDRTLDR
They are tests. As in TDD, we use test to drive the
design of the so ware
Usually, on a higher level than TDD
Written in a natural lenguage , like English
Example
3 . 5

12. TLDRTLDR
They are tests. As in TDD, we use test to drive the
design of the so ware
Usually, on a higher level than TDD
Written in a natural lenguage , like English
Example
3 . 5

13. TLDRTLDR
They are tests. As in TDD, we use test to drive the
design of the so ware
Usually, on a higher level than TDD
Written in a natural lenguage , like English
Example
3 . 5

14. TARGET: SHARE KNOWLEDGETARGET: SHARE KNOWLEDGE
A natural lenguaje:
Is used for all of us
Everyone can define, debate o improve a test
Allow all the team to discuss on tipically conflictive
topics: edge cases, exceptions...
3 . 6

15. TARGET: SHARE KNOWLEDGETARGET: SHARE KNOWLEDGE
A natural lenguaje:
Is used for all of us
Everyone can define, debate o improve a test
Allow all the team to discuss on tipically conflictive
topics: edge cases, exceptions...
3 . 6

16. TARGET: SHARE KNOWLEDGETARGET: SHARE KNOWLEDGE
A natural lenguaje:
Is used for all of us
Everyone can define, debate o improve a test
Allow all the team to discuss on tipically conflictive
topics: edge cases, exceptions...
3 . 6

17. TARGET: SHARE KNOWLEDGETARGET: SHARE KNOWLEDGE
A natural lenguaje:
Is used for all of us
Everyone can define, debate o improve a test
Allow all the team to discuss on tipically conflictive
topics: edge cases, exceptions...
3 . 6

18. EXECUTABLE SPECIFICATIONSEXECUTABLE SPECIFICATIONS
Using this test as specifications for our so ware, we
get specifications written on a plain english, but
executables.
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19. EXECUTABLE SPECIFICATIONSEXECUTABLE SPECIFICATIONS
Using this test as specifications for our so ware, we
get specifications written on a plain english, but
executables.
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20. HOW CAN YOU "EXECUTE" ENGLISH?HOW CAN YOU "EXECUTE" ENGLISH?
Transform a plain english specification in a test
Example
3 . 8

21. NOW WE HAVE TESTS!NOW WE HAVE TESTS!
But, obviously, we need to implement the code. No
black magic
Before that, lets review a few details about files and
organization.
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22. GHERKINGHERKIN
The format used in this specification is called Gherkin
There are just a few words that have a special
meaning: Feature, Scenario, Given, When y
Then.
(Also And, But)
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23. FEATUREFEATURE
Every feature is a capacity of our product. Each
feature must have its own .feature file
The keyword Feature must go at the begining, and
gives us the opportunity to descrive the feature in
one line
The rest of text between the feature line and the first
scenario can be used to describe the feature with
more detail
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24. SCENARIOSCENARIO
Usually, a feature has more than one scenario,
because we are interested on testing diferent
aspects: changing conditiones, edge cases, different
inputs, etc...
Every diferent case is defined with the keyboard
Scenario
As a rule, every scenario is a complete and concrete
example of a feature
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25. GIVENGIVEN
Given put our system in a known and controled
state, before the first intereaction.
(No user interactions if this part)
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26. WHENWHEN
When This is where we describe the actions the user
or external system wants to do. This must yield
some changes in the system.
Or maybe not
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27. THENTHEN
Then This is where we check that the outcomes of
our system are the expected
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28. AND Y BUTAND Y BUT
And y But are alternative versions of Given and Then
just to get a better feeling of proper english.
So, instead of writing:
We can write:
Given I have 10000€ in my current acount
Given I have 300€ in my saving accout
Given I have 10000€ in my current acount
And I have 300€ in my saving accout
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29. GO BACK TO PRACTICEGO BACK TO PRACTICE
LETS IMPLEMENT THE TESTLETS IMPLEMENT THE TEST
Example
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30. A FEW INTERESTING DETAILSA FEW INTERESTING DETAILS
ON STEPSON STEPS
The name of the function used to implemente the
steps it's not important!
Behave decide what funciones to call, and when,
based only in the text of decorator
Main idea is having reusable steps
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31. A FEW INTERESTING DETAILSA FEW INTERESTING DETAILS
ON STEPSON STEPS
The name of the function used to implemente the
steps it's not important!
Behave decide what funciones to call, and when,
based only in the text of decorator
Main idea is having reusable steps
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32. A FEW INTERESTING DETAILSA FEW INTERESTING DETAILS
ON STEPSON STEPS
The name of the function used to implemente the
steps it's not important!
Behave decide what funciones to call, and when,
based only in the text of decorator
Main idea is having reusable steps
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33. REQUESTREQUEST
Every step has a common first parameter called
request, that could be used for Sharing data
This data can be shared at a feaure level or a
scenario level
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34. REQUESTREQUEST
Every step has a common first parameter called
request, that could be used for Sharing data
This data can be shared at a feaure level or a
scenario level
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35. PARAMETER CAPTUREPARAMETER CAPTURE
One interesting ability is to "capture" some part of
the text of the step
This allow us to have parametrizable, and hence,
more reusable steps
Lets see this with another example
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36. DIFFERENCES WITH TDDDIFFERENCES WITH TDD
Emphasis is not in the code, but in the functionality
Specification is written in natural language (i.e.
english)
Spoken by all the members of the team: Developers
testers, Q/A, product owners, skateholders, users...
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37. DIFFERENCES WITH TDDDIFFERENCES WITH TDD
Emphasis is not in the code, but in the functionality
Specification is written in natural language (i.e.
english)
Spoken by all the members of the team: Developers
testers, Q/A, product owners, skateholders, users...
3 . 21

38. DIFFERENCES WITH TDDDIFFERENCES WITH TDD
Emphasis is not in the code, but in the functionality
Specification is written in natural language (i.e.
english)
Spoken by all the members of the team: Developers
testers, Q/A, product owners, skateholders, users...
3 . 21

39. DIFFERENCES WITH TDDDIFFERENCES WITH TDD
Emphasis is not in the code, but in the functionality
Specification is written in natural language (i.e.
english)
Spoken by all the members of the team: Developers
testers, Q/A, product owners, skateholders, users...
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40. PRACTICEPRACTICE
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41. A FEATURE FILE EXAMPLEA FEATURE FILE EXAMPLE
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42. Feature: Transfer between accounts
Scenario: Add savings
Given I have 10.000€ in my current acount
And I have 300€ in my saving accout
When I transfer 200€ from current to saving
Then I should have 9.800€ in my current acount
And I should have 500€ in my saving acount
◀
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43. INSTALL BEHAVEINSTALL BEHAVE
Behave is a BDD tool written in Python
We will see other options for other languages at the
end of the talk
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44. pip install behave
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45. FOR OUR FIRST BDD TEST...FOR OUR FIRST BDD TEST...
WE ARE GOING TO NEED ...WE ARE GOING TO NEED ...
A features directory
Inside:
a directory named steps.
And a file named with extension
.feature*
* with the content show in the previous example
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46. FOR OUR FIRST BDD TEST...FOR OUR FIRST BDD TEST...
WE ARE GOING TO NEED ...WE ARE GOING TO NEED ...
A features directory
Inside:
a directory named steps.
And a file named with extension
.feature*
* with the content show in the previous example
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47. FOR OUR FIRST BDD TEST...FOR OUR FIRST BDD TEST...
WE ARE GOING TO NEED ...WE ARE GOING TO NEED ...
A features directory
Inside:
a directory named steps.
And a file named with extension
.feature*
* with the content show in the previous example
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48. FOR OUR FIRST BDD TEST...FOR OUR FIRST BDD TEST...
WE ARE GOING TO NEED ...WE ARE GOING TO NEED ...
A features directory
Inside:
a directory named steps.
And a file named with extension
.feature*
* with the content show in the previous example
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49. mkdir features
mkdir features/steps
vim features/transfer-between-accounts.feature
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50. FIRST TEST WRITTEN!FIRST TEST WRITTEN!
AND IT IS EXECUTABLE!AND IT IS EXECUTABLE!
To execute it, just type on the command line:
behave
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51. Feature: Transfer between accounts # features/transfer-between
Scenario: Add savings # features/t
Given I have 10000€ in my current acount # None
And I have 300€ in my saving accout # None
When I transfer 200€ from current to saving # None
Then I should have 9800€ in my current acount # None
And I should have 500€ in my saving acount # None
Failing scenarios:
features/transfer-between-accounts.feature:3 Add savings
0 features passed, 1 failed, 0 skipped
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52. You can implement step definitions for undefined steps with th
@given(u'I have 10000€ in my current acount')
def step_impl(context):
raise NotImplementedError(u'STEP: Given I have 10000€ in m
@given(u'I have 300€ in my saving accout')
def step_impl(context):
raise NotImplementedError(u'STEP: Given I have 300€ in my
@when(u'I transfer 200€ from current to saving')
def step_impl(context):
raise NotImplementedError(u'STEP: When I transfer 200€ fro
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53. IT WORKS!IT WORKS!
And It even gives us a scheleton of the functions we
need to implement to run the tests
◀
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54. A SIMPLE TESTA SIMPLE TEST
Let's see a first implementation
Given thath we have no real code to test for now,
use a simulation
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55. GIVEN...GIVEN...
#!/usr/bin/env python
from behave import *
@given("I have 10000€ in my current acount")
def step_impl(context):
context.current_account = 10000
@given("I have 300€ in my saving accout")
def step_impl(context):
context.savings_account = 300
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56. WHEN...WHEN...
@when("I transfer 200€ from current to saving")
def step_impl(context):
context.savings_account += 200
context.current_account -= 200
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57. THEN...THEN...
@then("I should have 9800€ in my current acount")
def step_impl(context):
assert context.current_account == 9800
@then("I should have 500€ in my saving acount")
def step_impl(context):
assert context.savings_account == 500
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58. EXECUTE BEHAVEEXECUTE BEHAVE
Feature: Transfer between accounts # features_002/transfer-bet
Scenario: Add savings # features_0
Given I have 10000€ in my current acount # features_0
And I have 300€ in my saving accout # features_0
When I transfer 200€ from current to saving # features_0
Then I should have 9800€ in my current acount # features_0
And I should have 500€ in my saving acount # features_0
1 feature passed, 0 failed, 0 skipped
1 scenario passed, 0 failed, 0 skipped
5 steps passed, 0 failed, 0 skipped, 0 undefined
Took 0m0.000s
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59. A bit more Theory
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60. PARAMETRIZABLE STEPSPARAMETRIZABLE STEPS
We can parse the example text strings and get
information for the steps
The library is used by default
parse defines itself as the opposite of format()
parse
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61. Change definition of first step from:
To:
@given("I have 10000€ in my current acount")
def step_impl(context):
context.current_account = 10000
@given("I have {amount}€ in my current acount")
def step_impl(context, amount):
context.current_account = int(amount)
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62. Feature: Transfer between accounts # features_003/transfer-bet
Scenario: Add savings # features_0
Given I have 10000€ in my current acount # features_0
And I have 300€ in my saving accout # features_0
When I transfer 200€ from current to saving # features_0
Then I should have 9800€ in my current acount # features_0
And I should have 500€ in my saving acount # features_0
1 feature passed, 0 failed, 0 skipped
1 scenario passed, 0 failed, 0 skipped
5 steps passed, 0 failed, 0 skipped, 0 undefined
Took 0m0.001s
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63. WE CAN EVEN FORGETWE CAN EVEN FORGET
ABOUT THE INTEGER CASTABOUT THE INTEGER CAST
@given("I have {amount:d}€ in my current acount")
def step_impl(context, amount):
context.current_account = amount
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64. BEHAVE HAVE ALTERNATIVE PARSERSBEHAVE HAVE ALTERNATIVE PARSERS
parse is used by default
cfparse let us work with
cardinality
re to use regular expressions
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65. BEHAVE HAVE ALTERNATIVE PARSERSBEHAVE HAVE ALTERNATIVE PARSERS
parse is used by default
cfparse let us work with
cardinality
re to use regular expressions
4 . 22

66. BEHAVE HAVE ALTERNATIVE PARSERSBEHAVE HAVE ALTERNATIVE PARSERS
parse is used by default
cfparse let us work with
cardinality
re to use regular expressions
4 . 22

67. BEHAVE HAVE ALTERNATIVE PARSERSBEHAVE HAVE ALTERNATIVE PARSERS
parse is used by default
cfparse let us work with
cardinality
re to use regular expressions
4 . 22

68. BUT BEFORE...BUT BEFORE...
Lets forget all this financial stuff nobody cares
for...
and use more interesting examples...
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69. POKEMONPOKEMON
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70. TABLE EXAMPLESTABLE EXAMPLES
We can add data to the steps in a tabular form
Feature: Pokemon search
Scenario: Find the weakest
Given I have this pokemons
|name | attack | defense |
|psyduck | 20 | 60 |
|torchic | 20 | 60 |
|spinda | 10 | 80 |
|lillipup | 10 | 50 |
When I search for the one with less defense
Then I should get lillipup
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71. WE CAN PROCESS THIS TABLEWE CAN PROCESS THIS TABLE
IN THE STEP CODEIN THE STEP CODE
@given('I have this pokemons')
def step_impl(context):
for row in context.table:
pokemon = Pokemon(
row['name'],
attack=row['attack'],
defense=row['defense'],
)
setattr(context, row['name'], pokemon)
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72. WE CAN HAVE SHARED PRECONDITIONSWE CAN HAVE SHARED PRECONDITIONS
FOR ALL THE STEPSFOR ALL THE STEPS
Feature: Transfer between accounts
Background:
Given I have this pokemons
|name | attack | defense |
|psyduck | 20 | 60 |
|torchic | 20 | 60 |
|spinda | 10 | 80 |
|lillipup | 10 | 50 |
Scenario: Search for the weakest
When I search for the one with less defense
Then I should get lillipup
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73. TAGSTAGS
Selection of scenarios or features
Can select for one or several tags
Can execute the ones not having one or more
tags
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74. TAGSTAGS
Selection of scenarios or features
Can select for one or several tags
Can execute the ones not having one or more
tags
4 . 28

75. TAGSTAGS
Selection of scenarios or features
Can select for one or several tags
Can execute the ones not having one or more
tags
4 . 28

76. TAGSTAGS
Selection of scenarios or features
Can select for one or several tags
Can execute the ones not having one or more
tags
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77. FEATURE WITH TAGSFEATURE WITH TAGS
Asuming this feature and sample data
Feature: Search pokemons
Background:
Given I have this pokemons
|name | attack | defense |
|psyduck | 20 | 60 |
|torchic | 20 | 60 |
|trapinch | 20 | 60 |
|spinda | 10 | 80 |
|lillipup | 10 | 50 |
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78. AND THIS STEPSAND THIS STEPS
@fight
Scenario: Search for the weakest
When I search for the one with less defense
Then I should get lillipup
@fight
Scenario: Search for the stronger
When I search for the one with more attack
Then I should get spinda
Scenario: Search for name
When I search for the letter t
Then I should get torchic
And I should get trapinch
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79. EXECUTINGEXECUTING
JUST THE FIGHT SCENARIOSJUST THE FIGHT SCENARIOS
behave features_006 --tags=fight
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80. EXECUTINGA ALL THE SCENARIOSEXECUTINGA ALL THE SCENARIOS
BUT THE FIGHT ONESBUT THE FIGHT ONES
behave features_006 --tags=-fight
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81. WORKS IN PROGRESSWORKS IN PROGRESS
run with -w flag
turns off stdout capture
turns off logging capture
turns off pretty output
only runs scenarios tagged with
“@wip”
stops at the first error
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82. TO BE HANDLE WITH CARETO BE HANDLE WITH CARE
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83. RECOMENDATIONSRECOMENDATIONS
Don't mix features
One scenario to test just one case
it's code, store it in the repo
High level descriptions: Do not use technology
terms
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84. DANGERSDANGERS
Don't make the system too complex
Don't get used to having some tests never passsing
Don't start testing the easy ones. You must go for the
ones that teaches you the most
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85. DANGERSDANGERS
Don't make the system too complex
Don't get used to having some tests never passsing
Don't start testing the easy ones. You must go for the
ones that teaches you the most
5 . 3

86. DANGERSDANGERS
Don't make the system too complex
Don't get used to having some tests never passsing
Don't start testing the easy ones. You must go for the
ones that teaches you the most
5 . 3

87. DANGERSDANGERS
Don't make the system too complex
Don't get used to having some tests never passsing
Don't start testing the easy ones. You must go for the
ones that teaches you the most
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88. RULE NUMBER 1 ON ANALISYS CLUBRULE NUMBER 1 ON ANALISYS CLUB
Don't tell me your solution
Instead, tell me your
problem
(Rule number 2 is Everybody lies, if you are interested)
5 . 4

89. TOOLS AND OPTIONSTOOLS AND OPTIONS
Ruby - Cucumber
Javascript -
Cucumber.js
.Net - xBehave
Java - JBehave
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90. THANK YOU!THANK YOU!
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